1. Field of the Invention
The present invention relates to optical semiconductor devices for use in optical communications, which output laser beams exhibiting low wavelength variation over time. In particular, the present invention relates to a package of a semiconductor laser device which outputs light having a wavelength of 1.1 μm or more.
2. Description of the Related Art
Semiconductor lasers that output light having a wavelength of 1.1 μm or more are widely used as light sources for optical communications using optical fibers or free space as the transmission medium and as light sources for use in scientific and industrial analysis and measurement. In operation, the semiconductor laser is hermetically sealed in the interior of a package in order to prevent deterioration due to environmental factors and contamination caused by foreign matter.
In a known optical semiconductor device comprising a semiconductor laser hermetically sealed in the interior of a package, an inert gas such as nitrogen or helium which has a low reactivity to semiconductor lasers is filled in the interior of the package.
In optical communications, even slight wavelength variation in the light source deteriorates the quality of the communication. Thus, in optical semiconductor devices for use in optical communications, the variation in the output wavelength of the semiconductor lasers needs to be suppressed as much as possible.
Moreover, light having a wavelength of 1.1 μm or more is used in various scientific and industrial analyses and measurements as well as optical communications. In such applications, suppression of the wavelength variation is also important from the point of view of improving the accuracy of the analysis and measurement.